rt: Remove `threaded_scheduler()` and `basic_scheduler()` (#2876)

Co-authored-by: Alice Ryhl <alice@ryhl.io>
Co-authored-by: Carl Lerche <me@carllerche.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/tokio/src/blocking.rs b/tokio/src/blocking.rs
new file mode 100644
index 00000000..d6ef5915
--- /dev/null
+++ b/tokio/src/blocking.rs
@@ -0,0 +1,48 @@
+cfg_rt_core! {
+    pub(crate) use crate::runtime::spawn_blocking;
+    pub(crate) use crate::task::JoinHandle;
+}
+
+cfg_not_rt_core! {
+    use std::fmt;
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    pub(crate) fn spawn_blocking<F, R>(_f: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        assert_send_sync::<JoinHandle<std::cell::Cell<()>>>();
+        panic!("requires the `rt-core` Tokio feature flag")
+
+    }
+
+    pub(crate) struct JoinHandle<R> {
+        _p: std::marker::PhantomData<R>,
+    }
+
+    unsafe impl<T: Send> Send for JoinHandle<T> {}
+    unsafe impl<T: Send> Sync for JoinHandle<T> {}
+
+    impl<R> Future for JoinHandle<R> {
+        type Output = Result<R, std::io::Error>;
+
+        fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+            unreachable!()
+        }
+    }
+
+    impl<T> fmt::Debug for JoinHandle<T>
+    where
+        T: fmt::Debug,
+    {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            fmt.debug_struct("JoinHandle").finish()
+        }
+    }
+
+    fn assert_send_sync<T: Send + Sync>() {
+    }
+}